The conversion of ethers to their corresponding alkenes and alkanols (aliphatic alcohols) is an important reaction in a number of commercial processes. This reaction is used, by way of example, to remove isopropyl ether (IPE) produced as the by-product of the hydration of propylene to produce isopropyl alcohol (IPA or isopropanol). In addition, an important route for the production of tertiary olefins involves reaction of mixed olefins with an alcohol over an acid catalyst to selectively produce a tertiary alkyl ether, separation of the ether from the remaining olefin stream, and then decomposition of the ether to the desired tertiary olefin. This latter process relies on the fact that tertiary olefins react with alcohols more rapidly than either secondary or primary olefins and hence provides an effective method for extracting tertiary olefins, such as isobutene and isoamylene, from a mixed olefin stream. For the purposes of this invention, a tertiary olefin or isoolefin will be understood to be an olefin containing at least one carbon atom that is covalently bonded to three other carbon atoms.
Various catalysts have been proposed for the selective decompostion of ethers. See for example U.S. Pat. No. 4,691,073, U.S. Pat. No. 4,254,290, U.S. Pat. Nos. 4,320,232 and 4,521,638, U.S. Pat. No. 4,398,051, U.S. Pat. No. 4,357,147. “Production D'Isobutene de Haute Puretépar Décomposition du MTBE” by P. B. Meunier et al. in Revue de L'Institut Francais du Petrole, vol. 46, No. 3, May 1991, pages 361 to 387, U.S. Pat. No. 5,254,785, U.S. Pat. No. 5,177,301, U.S. Pat. No. 5,171,920 and Japanese Published Patent Application No. JP-A-06072904.
Japanese Published Patent Application No. JP-A-59010528, published Jan. 20, 1984, describes a process for thermally decomposing a tertiary ether to a tertiary olefin in the presence of a titanium or zirconium oxide catalyst containing 0.1 to 20 wt % of SO4−2 groups. The catalyst activity is said to be high even at low temperatures thereby allowing co-production of the corresponding alcohol with negligible etherification.
U.S. Pat. No. 5,607,892 discloses a zirconium/cerium mixed oxide having a specific surface area of greater than 10 m2/g. The mixed oxide is produced by intimately admixing a zirconium sol with a cerium sol, wherein the ratio of the mean diameter r1 of the particles of the zirconium sol to the mean diameter r2 of the particles of the cerium sol is at least 5, adding a precipitating amount of a base, such as aqueous ammonia, sodium hydroxide, or potassium hydroxide to the mixture, recovering the precipitate thus formed and calcining the precipitate at a temperature of 700 to 1,000° C. The mixed oxide is said to be useful as a catalyst or catalyst support for carrying out a variety of reactions, such as dehydration, hydrosulfurization, hydrodenitrification, desulfurization, hydrodesulfurization, dehydrohalogenation, reforming, steam reforming, cracking, hydrocracking, hydrogenation, dehydrogenation, isomerization, dismutation, oxychlorination, dehydrocyclization of hydrocarbons or other organic compounds, oxidation and/or reduction reactions, the Claus reaction, treatment of exhaust gases emanating from internal combustion engines, demetallation, methanation or shift conversion.
U.S. Pat. No. 6,150,299 discloses a cerium- and zirconium-based mixed oxide containing sulfur, which is said to be active as an exhaust gas purification catalyst and which comprises 50 to 79% by weight cerium oxide, 20 to 49% by weight zirconium oxide and 1 to 5% by weight sulfate (SO4). In Example 1, the mixed oxide was produced by dispersing cerous sodium sulfate double salt (containing 75 g as cerium oxide) in 1,000 g of water and adding an aqueous solution of zirconium nitrate (containing 25 g as zirconium oxide). Then, an aqueous solution of sodium hydroxide was added until the pH of the mixture became 13.5, whereby a precipitate was obtained. This precipitate was separated from the mixture and heated in the air at 600° C. for 5 hours. Analysis showed the resultant mixed oxide to contain 73.9% by weight cerium oxide, 24.1% by weight zirconium oxide and 2.0% by weight sulfate.
International Patent Publication No. WO 03/37506, published May 8, 2003, discloses a promoter or catalyst support for an automobile exhaust gas system comprising a zirconium-cerium-based mixed oxide produced by reacting an alkali with an aqueous solution of a zirconium salt containing 0.42-0.7 mole of sulfate anion per mole of zirconium cation at a temperature not greater than 50° C. in the presence of a cerium salt to form a mixed cerium-zirconium hydroxide and then calcining the hydroxide at a temperature of 500 to 1000° C., such as 650 to 850° C.
U.S. Pat. No. 6,124,232 discloses a tungsten-modified zirconia catalyst produced by coprecipitating zirconia with an anion or oxyanion of tungsten in the presence of ammonium sulfate to obtain a sulfate-containing product, steaming the sulfate-containing product; recovering the sulfate-containing product by filtration, washing the product with water in order to remove the sulfate ions and calcining the product to produce a catalyst that is essentially free of sulfate ions. The catalyst is said to be active in the isomerization of paraffins.
U.S. Pat. No. 6,162,757 discloses a synthesis of a solid acid containing zirconium, in addition to a rare earth element, such as cerium, useful for isomerization of paraffins, ring opening of cyclics, hydrocracking, alkylation, hydrogenation of polynuclear aromatics, selective catalytic reduction of nitrogen peroxides, and oligomerization of light olefins.
U.S. Pat. No. 6,297,406 discloses a process for producing phenol and acetone from cumene hydroperoxide, in which cumene hydroperoxide is contact with a solid acid catalyst comprising a mixed oxide of cerium and a Group IVB metal.
Unpublished International Application No. PCT/US2004/041546 discloses a process for selectively converting a dialkyl ether to the corresponding alkene and alkanol, the process comprising contacting a feed containing at least one dialkyl ether with a catalyst comprising an acidic mixed metal oxide having the following composition:XmYnZpOq where X is at least one metal selected from Group 4 of the Periodic Table of Elements, Y is at least one metal selected from Group 3 (including the Lanthanides and Actinides) and Group 6 of the Periodic Table of Elements and Z is at least one metal selected from Groups 7, 8, and 11 of the Periodic Table of Elements; m, n, p and q are the atomic ratios of their respective components and, when m is 1, n is from 0.01 to 0.75, p is from 0 to 0.1, and q is the number of oxygen atoms necessary to satisfy the valence of the other components. The mixed oxides preferably contain sulfur, typically present in an amount of up to 5 wt %, such as up to 1 wt %, of the final mixed oxide composition. The mixed oxides can be prepared by impregnation or by co-precipitation from a liquid mixture containing a source of Group 4 metal ions and a source of Group 3 and/or Group 6 metal ions.
Ceria-zirconia catalysts and the like have also been found useful for the purification of exhaust gases, such as produced by an internal combustion engine. Such processes and catalyst made therefore have been described in, for instance, U.S. Pat. Nos. 5,478,543; 5,518,699; 5,532,198; 5,580,536; 5,582,785; 5,607,892; 5,712,218; 5,747,401; 5,908,800; 6,133,194; 6,150,299; 6,255,242; 6,291,719; 6,319,876; 6,506,705, and 6,605,565
The present invention provides an improved method of making Group 3 and Group 4 mixed metal oxides, particularly cerium-zirconium mixed metal oxides suitable for catalyzing the decomposition of ethers to alkenes and alkanols.